Although never involved in war, three major incidents occurred during Onslow's career. The first occurred in 1972, when a disgruntled sailor who disobeyed orders caused the submarine to dive to almost twice her safe operating depth.[3] As a result, the RAN changed the Submarine Service from being able to "conscript" any sailor for submarine service to volunteer only.[3]. The general consensus from a number of submariners who served on Onslow during the early 1970s is that this event did not happen.

The second happened in 1981, when carbon monoxide fumes from one of the diesel generators filled the submarine, resulting in the death of one sailor.[4] Although changes were made to submarine operating procedures, the boat's company was not provided with any psychological counselling, and the incident report remained classified until 2009.[4] The third was a controversial line-crossing ceremony in 1995, which resulted in restrictions being placed on similar ceremonies aboard RAN vessels.[5][6] During her career, Onslow became the first conventionally powered submarine to be fitted with anti-ship missiles, and was successful in wargames: "sinking" a seven-ship flotilla during Exercise Kangaroo 3 in 1980, and the United States supercarrier USS Carl Vinson at RIMPAC 1998.[3][7][8][9]

The submarine is 295.2 feet (90.0 m) long, with a beam of 26.5 feet (8.1 m), and a draught of 18 feet (5.5 m) when surfaced.[1] At full load displacement, Onslow displaces 2,030 tons when surfaced, and 2,410 tons when submerged.[1] The two propeller shafts are each driven by an English Electric motor providing 3,500 brake horsepower and 4,500 shaft horsepower; the electricity for these is generated by two Admiralty Standard Range supercharged V16 diesel generators.[2] These could propel the submarine at up to 12 knots (22 km/h; 14 mph) on the surface, and up to 17 knots (31 km/h; 20 mph) when submerged.[1]Onslow had a maximum range of 9,000 nautical miles (17,000 km; 10,000 mi) at 12 knots (22 km/h; 14 mph), and a test depth of 200 metres (660 ft) below sea level.[1][2] When launched, the boat had a company of 8 officers and 56 sailors, but by the time she decommissioned, the number of sailors had increased to 60.[1][2] In addition, up to 16 trainees could be carried.[2]

Unlike other submarines in her class, Onslow was fitted with a four-man diver access hatch, allowing for easier deployment and recovery of special forces divers.[12]

The main armament of Onslow was six 21-inch (53 cm) bow torpedo tubes, capable of firing torpedoes or releasing sea mines.[1] The British Mark 8 torpedo was initially carried by the submarine; this was replaced by the wire-guidedMark 23.[13] During a refit from 1982 to 1984, Oberon became the first conventionally powered submarine in the world to be fitted with anti-ship missiles; specifically the UGM-84 Sub Harpoon.[7][8] At the same time, the Mark 23 torpedoes were replaced by the United States Mark 48 wire-guided torpedo.[7] As of 1996, the standard payload of Onslow was a mix of 20 Mark 48 Mod 4 torpedoes and Sub Harpoon missiles.[1] Some or all of the torpedo payload could be replaced by Mark 5 Stonefish sea mines, which were deployed through the torpedo tubes.[13]

The submarine's secondary armament consisted of two stern-mounted, short-length 21-inch (53 cm) torpedo tubes: these were intended for use against pursuing submarines, but the development of steerable wire-guided torpedoes shortly after the boat entered service made these redundant, and they were closed off during the 1982-84 refit.[14] The aft tubes fired Mark 20 anti-submarine torpedoes.[14]

Onslow arrived in Sydney at the conclusion of her delivery voyage to Australia on 4 July 1970.[11] On board was Vice Admiral Sir Victor Smith, at the time the Chief of Naval Staff, who had embarked at Brisbane.[11] The boat visited Pearl Harbor later that year; arriving without being detected by the USN until she surfaced in the middle of the harbour.[15]Onslow returned to Pearl Harbor in 1971 to participate in the RIMPAC multinational naval exercise.[16] During the exercise, a practice torpedo fired by the United States Coast Guard Cutter Rush[17] failed to disengage as designed and hit the submarine—the only damage was a small dent near the stern.[16]

In 1972,[clarification needed] the first major incident of Onslow's career occurred. The submarine was performing dive tests off the continental shelf outside Sydney Heads.[3] One of the boat's company, transferred to the RAN Submarine Service against his will, refused to obey an order to close the valve on forward ballast tank, causing it to overfill with seawater and forcing the submarine into a steep crash dive.[3] The dive took Onslow to a depth of 366 metres (1,201 ft), well beyond the 200-metre (660 ft) safe operating depth of the Oberon class, before another sailor was able to close the valve.[3] Seven tons of water had been taken on by the ballast tank, and with not enough compressed air available to completely empty the tank and allow the submarine to rise, Onslow's company had to rely on the submarine's twin propeller screws to help make it to the surface.[3] The sailor responsible for the incident was beaten by his comrades and removed from the submarine in a straitjacket upon the boat's return to submarine base HMAS Platypus.[3] This incident led the RAN to change submarine service to volunteers only.[3]

Onslow became the first vessel of the RAN to be assigned to the ANZUK force in Singapore on 22 July 1972.[18] During another ANZUK deployment, in 1974, the boat's attack periscope was damaged when it came in contact with the log probe of the frigate HMS Leopard.[citation needed] The boat returned to Australia on 18 December.[18] On 5 May 1975, Onslow began a two-year refit at Cockatoo Island Dockyard, becoming the first Australian submarine to use the dockyard's new slave dock.[19] This dock had been built specifically for refit work on Oberon-class submarines, and was the main location of all Onslow's refits until 1990.[19] In 1977, Onslow was presented with the Gloucester Cup, marking her as the most efficient warship in the RAN during the previous year—Onslow was the first submarine to receive the award.[16]

Onslow underway on the surface. A sailor is standing near the original bow sonar dome. This dome was replaced during the submarine's 1982–84 refit, as the new sonar was larger.

The second major incident of the boat's career happened on 1 March 1981, when Onslow was participating in wargames with a Royal New Zealand Navy frigate off the coast of Sydney.[4] While operating at periscope depth, the submarine spotted an 'enemy' P-3C Orion aircraft[verification needed] and stopped snorting (the process of taking in air to operate the boat's two diesel generators and expelling the produced exhaust through a snorkel) in preparation to go deep.[4] Both generators were turned off, but upon diving, it was quickly discovered that the starboard diesel had failed to switch off or had restarted and as the exhaust snorkel was sealed, the carbon monoxide exhaust filled the submarine.[4]Onslow rapidly resurfaced, and the exhaust was pumped from the submarine.[4] Able Seaman Christopher Passlow, who had been on the lower deck of the submarine at the time, died of asphyxiation and carbon monoxide poisoning, while another eighteen were rendered unconscious or were convulsing because of blood poisoning.[4][20] Upon returning to base, doctors found that one-third of the 66 survivors had absorbed twice the lethal limit of carbon monoxide into their blood.[4] The company was given a week's leave, with no further assistance from the RAN; psychological or otherwise.[4] Two submariners were later awarded decorations for bravery.[21]

The RAN Board of Inquiry into the incident concluded that the accident was caused by human error—the duty engineer failed to shut down both engines—but members of Onslow's complement disagree with this, claiming the problem to be mechanical in origin.[4] Changes were made to Submarine Service operating procedures as a result of the Inquiry, but the investigation and subsequent report remained classified until 2009, when the information was acquired by the Sunday Nightnewsmagazine program under the Freedom of Information Act.[4] When interviewed by Sunday Night in March 2009, the deputy Chief of Navy, Rear Admiral Davyd Thomas (who had been Passlow's divisional officer prior to the incident) promised counselling for the survivors, and claimed that prior treatment of the Onslow submariners was due to a limited understanding of post-traumatic stress disorder back in the 1980s.[4]

Onslow underwent a modernisation refit from 1982 until 1984; becoming the third Australian Oberon to be modernised.[7] As part of the modernisation, integrated data processing and fire control systems were installed, and the boat was fitted with Micropuffs passive ranging sonar.[22] The torpedo payload was upgraded to the United States Mark 48 wire-guided torpedo.[7] In addition to new torpedoes, the modernisation allowed Oberon-class submarines to carry and fire the Harpoon anti-ship missile through the torpedo tubes: Onslow became the first conventionally powered submarine in the world to be fitted with guided anti-ship missiles.[7][8]

Onslow's fin and equipment masts

Onslow was the first Australian submarine to visit the west coast of the United States of America when she arrived in San Diego on 17 July 1985.[23] The boat made goodwill visits to the cities of San Francisco and Seattle during mid-August, before participating in the Royal Fleet Review for the 75th anniversary of the Royal Canadian Navy.[11][24]

Onslow's "safe to dive" certificate ran out just after Christmas 1989.[25] The Australian government had been trialling a program whereby refit work was tendered out to the private sector; delays in selecting the winning company and allocating the funds meant that an 18-month refit of the submarine scheduled to begin at the start of 1990 did not commence on time.[25]Australian Defence Industries (ADI) was awarded the $100 million refit contract for Onslow and sister submarine HMAS Otama in July.[26] Cockatoo Island's slave dock was transferred to the ADI facilities at Garden Island in November 1990, and was used for the refit.[19] It was later found, during arbitration between the Australian Government and Cockatoo Island Dockyard for various issues, that by tendering out the submarine refits to other companies, the government was in breach of contract with the Dockyard; A$17.3 million in compensation was awarded to the dockyard in August 1996 for loss of profits and overhead costs.[27]

In the early 1990s, four of Onslow's sister boats were decommissioned from service. By 1996, Onslow and Otama were the only members of the class in active service.

During 1995, Onslow was deployed to South East Asia. During this deployment, the personnel of Onslow were involved in a controversial line-crossing ceremony while operating near the equator.[6] During this particular ceremony, normally intended to induct new sailors into the 'court of King Neptune', the victims were verbally and physically abused, had their pelvises and genitals covered in what was described as a "blistering concoction", then thrown overboard and forced to stay there until the rest of the company permitted them on board.[6] When one of the victimised sailors complained to superiors, he became subject to several administrative errors and inconveniences, to the point where he was forced to resign a year later.[6] The sailor acquired a copy of a videotape made of the ceremony and presented it to the Nine Network, which broke the story on 6 July 1999.[6] An inquiry into the incident aboard Onslow was held, which found that although guidelines had been developed in the years after the incident to prevent harassment in the Australian Defence Force, disciplinary charges against the sailors involved could not be laid, as more than three years had passed since the offence.[5] The inquiry also stated that while line-crossing ceremonies would continue to be held aboard RAN vessels, they would be supervised by a non-involved member of the crew to prevent similar extreme situations developing.[5] The deployment ended in December, with Onslow visiting her namesake town for the last time on her return to Australia.[28]

On the evening of 16 April 1997, three Australian Special Air Service Regiment soldiers were injured when they were thrown from their Zodiac boat during launch and recovery exercises with the submarine.[29] Later that year, in November, Onslow participated in a joint RAN-RAAF exercise off the coast of Western Australia.[30] Over the end of 1997 and the start of 1998, Onslow and Otama were used for trials of the Australian-designed Narama towed array sonar.[31] The Narama sonar was one of the towed arrays under consideration for incorporation with the under-development Collins-classsubmarines,[31] and was the array selected.

In mid-1998, the date of Onslow's decommissioning was announced for early 1999.[28] Representatives from the town of Onslow, Western Australia requested that the submarine visit her namesake town before decommissioning, but were informed that the submarine's planned operational schedule could not accommodate such a visit.[28] As part of this schedule, Onslow participated in the 1998 RIMPAC exercise.[3] The submarine had to pull out of the early part of the exercise: a resistor in the motor room switchboard had begun to smoke, forcing Onslow to return to Pearl Harbor for repairs.[32] She departed on 12 July, but was forced to return less than 24 hours later when a smouldering smell was noticed.[32] The boat's luck changed during the latter part of RIMPAC 98, when on the morning of 10 August, Onslow located the 'enemy' Nimitz-classUSS Carl Vinson, closed to within 300 metres (980 ft) without being detected, then released green flares to indicate her location, 'sinking' the supercarrier.[3][33] From 7 November onwards, Onslow was used as the target submarine for the annual Fincastle competition.[34]Onslow operated on a secret patrol course 130 nautical miles (240 km; 150 mi) south of Kangaroo Island while aircraft from the competing Australian, British, Canadian, and New Zealand air forces attempted to locate and 'sink' her.[34]No. 5 Squadron RNZAF was declared the winner, although all teams were successful in locating the submarine during at least one of their three attempts.[35]

Onslow was decommissioned from service on 30 March 1999.[36] While in service, Onslow travelled 358,068 nautical miles (663,142 km; 412,057 mi).[37] On the same day, sister boat Otama was permanently reassigned to the submarine base at HMAS Stirling in Western Australia, clearing the way for the closure of HMAS Platypus.[36]

On 22 November 2002, Onslow was taken by tugs to Garden Island for three weeks of maintenance in drydock.[41] This included cleaning and repainting of the hull,[42] replacement of the tributyltin coating used to prevent biofouling with a coating that was not harmful to marine organisms,[41] and the sealing of several ballast tanks to improve the boat's stability and raise the aft section relative to the waterline.[43]Onslow was returned to the museum on 11 December, and re-opened to the public three days later.[43] In October and November 2008, Onslow returned to Garden Island for maintenance and upkeep. During this refit, an additional torpedo was loaded into the submarine's torpedo tubes and her hull was cleaned and painted.[44] Another docking occurred on 18 May 2012, with hull cleaning, rust removal, repainting, and repairs to the boat's aft torpedo tubes done before she returned to display on 6 June.[45] In November 2015, the submarine was moved to the new Warships Pavilion 'Action Stations' at the Australian National Maritime Museum alongside HMAS Vampire (D11) and HMAS Advance. In February 2018 Onslow was towed from the museum to Garden Island, Sydney for regular maintenance in dry dock.